ALBANY – A powerful labor leader with strong ties to Sen. Hillary Clinton yesterday joined the growing ranks of Democrats bashing Caroline Kennedy as a possible successor to the former first lady in the US Senate.

“Caroline Kennedy, although I’m sure a fascinating and engaging person, simply doesn’t have the experience or Washington know-how to get it done for New York,” said Stuart Applebaum, president of the 100,000- member Retail, Wholesale and Department Store Union.

Applebaum, former chief house counsel to the Democratic National Committee and a Clinton delegate at the Democratic National Convention, blasted Kennedy for having failed to speak out against George W. Bush’s policies during the Republican president’s two terms.

“Her voice has barely been heard during these long last eight years as so many of us have worked hard against the policies of the Bush administration,” said Applebaum, described by prominent state Democrats as a “close ally” of Hillary and Bill Clinton.

“She is a blank slate on New York issues. We simply don’t know where she stands, what her priorities are for the state or if and who she will fight for,” Applebaum continued.

Insiders believe Clinton and her top allies don’t want Kennedy to be tapped for the Senate seat because of her strong backing of Barack Obama over Clinton during the Democratic primaries.

Applebaum’s sharply worded critique of Kennedy came as Rep. Nydia Velazquez of Brooklyn, considered by many to be a front-running contender for the Senate post, said she had told Gov. Paterson, who will name Clinton’s replacement, that she was withdrawing from consideration.

“While I have been proud and humbled to be considered, I have decided to stay as a senior member of the House of Representatives,” Velazquez said in a statement.

Applebaum’s blasts came a day after Attorney General Andrew Cuomo, a federal housing secretary under President Clinton who is on Paterson’s short list to replace Clinton, repeatedly declined to say whether he felt the daughter of John F. Kennedy was fit to hold the Senate seat.

Robert Zimmerman, a member of the Democratic National Committee and an important Clinton adviser and fund-raiser, told The Post this week that Kennedy had “not demonstrated the qualifications or the experience for the position.”

Zimmerman’s comments were similar to those made earlier in the week by Rep. Gary Ackerman, a Queens Democrat, comparing Kennedy’s credentials for the Senate to those of singer and actress Jennifer Lopez.

Paterson has said Kennedy called him to talk about the Senate post but never asked for the job.

Cuomo has repeatedly declined to say whether he’s interested in the job but appears to have ruled it out in private conversations with friends, sources said.